Every card can be played into a slot the normal way, or etched onto a blank face of either die. An etched face fires its card the instant that face is rolled — including on the very next roll this turn.
Scrape a face blank (2 energy) to clear it for something better. Scraping a numbered or elemental face costs you that match, but buys build space — that trade is the whole game.
At end of turn the number die picks which slot fires; if the element die matches that card as well, it fires twice. Twelve faces across two dice are your entire build — etch the same card twice to double its odds.